Three-phase flow occurs in many processes of great practical importance to reservoir engineering including in WAG (water alternating gas) and SWAG (simultaneous water and gas injection) processes. In such situations, accurate determination of relative permeability values to water, oil, and gas is crucial for prediction of the reservoir performance and estimation of oil recovery under these processes. Unfortunately, compared with two-phase relative permeabilities, measured three-phase relative permeability data are rare and prone to error. This results in considerable uncertainty in determining ultimate oil recovery for processes involving three-phase flow. This lack of measured three-phase relative permeability data is mainly due to significant difficulties in obtaining accurate three-phase laboratory data. Many models and correlations have been proposed for obtaining three-phase relative permeability values from two-phase ones, and some are available in commercial simulators. These are generally not based on sound physical understanding of three-phase flow and have been shown to be incapable of producing representative three-phase relative permeability data. This is, in particular, true for conditions involving mixed wettability, low-IFT and low oil saturations. Hysteresis and cyclic changes involved in the WAG and SWAG processes only add to the difficulties of the already complex problem of three-phase flow and its relative permeability determination.

At Heriot-Watt University we have been studying the physics of three-phase flow with particular attention to the WAG and SWAG processes since December 1997. In our well-equipped research laboratories we have high-pressure core facilities that have been used to carry out multiphase core flood experiments and measure fluid saturation profile within the core using x-ray techniques for many years.  We also have sophisticated high-pressure micromodel rigs that we have used over the past two decades to study the pore level mechanisms involved in multiphase flow including the depressurisation of waterflooded reservoirs and the WAG and SWAG processes accurately.  Immiscible and near miscible WAG and SWAG injection studies have been carried out successfully using models of different wettability.  Many pertinent flow parameters including the effects of trapped gas saturation and film flow and corner filament flow of oil and water have been observed, analysed and used to gather the pore scale physics for input to network modelling.

Project Progression

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Phase I

In Phase I of the research, micromodels of different wettability were used to study the basic physics of the WAG displacements. The results from these experimental observations were incorporated into a mathematical network simulator, which was used to generalise the experimental results to more realistic reservoir rock systems. In Phase I of the study the experiments were performed only at one value of pressure (one set of interfacial tension values).

Phase II

In Phase II of the project the work was extended to investigate the near-miscible WAG, simultaneous injection of water and gas (SWAG) and WAG injection at different values of pressure (IFT) as well as different rock wettability.

Phase III (2004-2007)

In Phase III (2004-2007) of the WAG project, we extended the work to coreflood experiments and performed a series of both 2-phase and 3-phase flow tests including WAG and SWAG. The measurements were mainly focused on a 1000 mD core of mixed-wettability using near-miscible fluids but also included some water-wet and immiscible experiments to form a basis for comparison. The majority of the tests were conducted with a very low gas-oil IFT of 0.04 mNm^-1 with some tests carried out at a higher gas-oil IFT of 3 mNm^-1 to determine the base case relative permeability curves.

In this phase we are continuing our study of WAG and SWAG processes, on low permeability cores, utilising the core facilities, simulation and mathematical modelling capabilities and the expertise available at Heriot-Watt University to further investigate the physics of the near miscible three-phase flow particularly in the WAG and SWAG processes for neutrally wet rocks. The study has two distinct and related parts:

High-pressure core experiments

Core test facilities capable of operating at simulated reservoir conditions to study three-phase flow, in-situ saturation measurements using x-ray and extensive fluid property measurements will be utilised to carry out WAG & SAWG tests.

Mathematical and Numerical Simulation

Simulators, comprising in-house fluid models and leading commercial simulators will be used to simulate and interpret experimental results. Experimental data will be used to evaluate the existing models and develop methodology for determining three phase relative permeability data for application in reservoir simulation.

The experience acquired in the process of WAG Phase 3 research, both on laboratory experiments and simulation will be very valuable in conducting the work in Phase 4.

Specific objectives include:

• To generate a comprehensive set of measured 2-phase and 3-phase relative permeability data.
• The data set would include measurements in two different cores under mixed-wet and natural water-wet conditions using a near-miscible gas-oil system.
• To evaluate the performance of the existing 3-phase relative permeability models against the in-house measurements.
• To develop a methodology to determine three-phase relative permeability data from the two-phase data applicable to mixed-wet rocks and near-miscibility conditions.
• To investigate the impact of interfacial tension, wettability, connate water saturation and petrophysical properties of the core on 3-phase relative permeability values and models.

Sponsor Area

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For more information about the project please contact Mehran Sohrabi. For current sponsors please access the sponsors area.